There are many, many kinds of coin operated devices and also many, many ways to attempt to cheat them. Several which come to mind are slugs, foreign coins, the retrievable coin-on-a-string, etc. As a result, there are many, many kinds of coin testing devices which attempt to discriminate between acceptable coins and those which are not.
The art is crowded with electrical, electronic and mechanical coin testing devices capable of fulfilling their purpose to a greater or lesser extent. Among the many approaches is the magnetic matching scheme described in Hinterstocker U.S. Pat. Nos. 3,599,771 and 3,741,363. Both patents deal with a three coil stack for creating a pair of magnetic fields in the two gaps between the three stacked coils. A sample coin is placed in one gap and a coin to be tested is passed through the second gap. Electronic circuitry monitors the magnetic fields to attempt to determine if the tested coin matches the sample coin using the attentuation characteristics of the coins as criteria.
The earlier issued patent describes a scheme whereby the testing electronics are switched on for only the brief instant when the coin is in test position. The later issued patent points out some of the problems with that approach and instead proposes a scheme which relies on sensing a null created when an acceptable coin passes through the magnetic field. Any coin which causes the system to null will be accepted unless the coin causes two nulls within a predetermined interval.
As commercially applied, the electronic coin tester described in those patents is used with a mechanical slug rejector, suggesting that the electronics does not do all of the testing.
In our co-pending U.S. application Ser. No. 387,820 filed June 14, 1982 there is disclosed a novel electronically controlled coin tester which needs no auxiliary mechanical devices, and which has superior selectability sensing not only the attentuation characteristics of the coins, but also the speed of travel of the tested coin.
As disclosed and claimed in our aforesaid application, the electronically controlled coin tester matches a tested coin against a sample coin held in a magnetic field by passing the test coin through a similar magnetic field to create a null in a detector coil sensing the fields. Electronic means monitors the duration and quality of the null as measures of the similarity of the coins and the magnetic field created with a spiked signal having a plurality of frequencies enhances selectability of the test coin.
Accordingly, it is an object of the present invention to provide an electronically controlled coin tester which enables matching a test coin against a sample coin in the aforementioned manner that permits the sample coin to be quickly and simply inserted and replaced. In this regard it is another object to provide an electronic coin tester of the foregoing type which can handle a wide range of coin diameters including the largest forms of coins circulated or used.
It is yet another object of the present invention to provide an electronically operated coin tester having provision to foil attempts to defeat the device by use of a proper coin on a wire or string.